OBJECTIVE To determine the efficacy of the plant extract Triptolide as a male contraceptive in a nonhuman primate species. RESULTS A protocol was devised to monitor reproductive endocrinology (testosterone and luteinizing hormone), behavior (to detect any changes in activity patterns or libido that may subsequently affect reproductive behavior and/or fertility), and reproductive physiology (sperm parameters quantified by a Hobsen Sperm Tracker; in vitro and in vivo fertility assessment) with minimal invasion and social disruption to marmoset subjects. The new marmoset fertility protocol included the development of an improved method of sperm collection for the marmoset vibrator stimulation. By modifying a Multicept FertiCare Personal Vibrator (which relies on vibrator-mediated penile afferent stimulation, designed to collect sperm from spinal cord injured men; also used successfully in squirrel monkeys), sperm samples were collected rapidly (less than 15 seconds) and reliably (80 - 100% success rate, depending on social housing conditions) from six male marmosets with minimal disturbance to their daily a ctivities. Sperm collection following vibrator stimulation was a significant improvement over the traditional sperm collection methods for marmosets, e.g. electroejaculation (30% success rate, requiring anesthesia) and vaginal washing (45-80% success rate, requiring long periods of single housing for females and time-consuming collection sessions). FUTURE DIRECTIONS To utilize our newly-developed assessment protocol to determine the efficacy of Triptolide as a male contraceptive in male marmosets. KEY WORDS male contraception, Triptolide, sperm, fertility, sperm collection, marmoset FUNDING CONRAD MFG-97-27